Yes 17.06c and latest MIXR release still uses 2.6 version, mainly because that code was developed long ago. I don't believe the 3.4.0 release is 100% compatible, so some rework would need to take place to move to that.
Given this, I'm very interested in transitioning away from protocol buffers and maybe to something more 'native' or easily integrated into software -- such as the cereal templates.
Thanks,
Doug
PS Yes, this is a good place for MIXR questions -- OpenEaagles has been renamed.